Toshiharu Matsuzawa

Study of proximity lithography simulations using measurements of dissolution rate and calculation of the light intensity distributions in the photoresist

This report describes the results of a study on resist profile simulation in proximity printing, using light intensity distribution and actually measured dissolution rate values, a method that takes the gap effect into consideration (the effect of the distance between mask and wafer on the aerial image and resist profiles). We calculate the light intensity distribution with the gap effect based on the Van Cittert-Zernike theory and on the Hopkins equation as a model of light intensity distribution of proximity printing in resist film. Dissolution rate values are obtained using an apparatus to measure resist film thickness during development. The resist profile simulation is carried out using the combined data thus obtained. To verify the validity of this simulation, we use an SEM to observe resist profiles obtained from a diazonaphthoquinone (DNQ)-novolak resin positive-type resist for thick films, varying the proximity gaps using the mask aligner, which uses light in the broadband wavelengths of 350 mm to 450 mm, and compare the results with the simulation. The results of simulation and those of the SEM observation are in agreement, proving the validity of our method.

Measurement of parameters for simulation of deep-UV lithography using an FT-IR baking system

A system for measurement of deprotection reaction parameters for use with chemically amplified (CA) resist was developed by incorporating baking equipment into a FTIR spectrometer. Using this system, studies were conducted of a new model based on previous deprotection reaction models, but including the effects of deprotection reaction delay and the presence of a quencher. Used in these studies were a t- BOC/PHS resist for KrF excimer laser exposure, and a TBMA0.33-IBMA0.33-MMA0.33 copolymer resin resists for ArF excimer laser exposure. Deprotection reaction parameters for this model were measured for these two resist. The resulting parameters were then used with the PROLITH/2 lithography simulator for profile calculations, which were compared with SEM observations, general tendencies agreed quite well. This finding indicates that the present model may be reasonably applied to CA resists intended for KrF and ArF excimer laser exposure, and confirms the usefulness of the systems described for deprotection reaction parameter measurement.

Measurement of Parameters for Simulation of 193 nm Lithography Using Fourier Transform Infrared Baking System.

By incorporating baking equipment into a Fourier transform infrared (FT-IR) spectrometer, a deprotection reaction parameter measurement system that can be used with chemically amplified resists has been developed. This system allows us to study new models for chemically amplified (CA) resists by including into a conventional deprotection reaction model an initial delay effect and a quencher effect. This model is also used to measure deprotection reaction parameters. The parameters thus obtained are inputted into a lithography simulator PROLITH/2 to perform profile simulations. The results are compared with those of scanning electron microscope (SEM) observations. Although the simulation results and SEM observations are not in complete agreement, the general trends observed are in adequate agreement. These results confirm the applicability of the proposed model to CA resists for ArF excimer laser lithography and verify the usefulness of the measurement system.

Resist metrology for lithography simulation, part I: exposure parameter measurements

The experimental measurement of the photoresist ABC modeling parameters is described and three different data analysis techniques are compared. The best technique, the use of full exposure simulation to fit the data, is shown to be more accurate than the conventional data analysis method over a wide variety of typical substrates. In particular, artificial swing curve like behavior is observed on non-ideal substrates using the standard data analysis, but is readily accounted for in the more accurate full simulation method.

Development of Photochemical Analysis System for F2-Excimer Laser Lithography Processes.

A system for photochemical analysis of F2-excimer laser lithography processes has been developed. The system, VUVES-4500, consists of 3 units: (1) an exposure and bake unit that uses the F2-excimer laser to carry out a flood exposure and then post-exposure bake (PEB), (2) a unit for measurement of the development rate of photoresists, and (3) a simulation unit that utilizes PROLITH of profile simulation software to calculate the resist profiles and process latitude using the measured development rate data. With this system, preliminary evaluation of the performance of F2-Excimer laser lithography can be performed without the use of a lithography tool capable of imaging and alignment. Profiles for 150 nm lines are simulated for the PAR-101 resist (manufactured by Sumitomo Chemical) and the SAL-601 resist (manufactured by Shipley), a chemically amplified resist that has sensitivity at the F2-excimer laser wavelength. The simulation successfully predicts the resist behavior. Thus it is confirmed that the system enables efficient evaluation of the performance of F2-excimer laser lithography processes.

Development of analysis system for F2-excimer laser photochemical processes

A system for photochemical analysis of F2-excimer laser lithography processes has been developed. The system, VUVES- 4500, consists of 3 units: (1) an exposure and bake unit that uses the F2-excimer laser to carry out a flood exposure and then post-exposure bake (PEB) of a resist coated wafer, (2) a unit for the measurement of development rate of photoresists, and (3) a simulation unit that utilizes PROLITH to calculate the resist profiles and process latitude using the measured development rate data. With this system, preliminary evaluation of the performance of F2 excimer laser lithography can be performed without a lithography tool that is capable of imaging and alignment. Profiles for 100 nm lines are simulated for the PAR-101 resist (manufactured by Sumitomo Chemical) and the SAL-601 resist (manufactured by Shipley), a chemically amplified resist that has sensitivity at the F2 excimer laser wavelength. The simulation successfully predicts the resist behavior. Thus, it is confirmed that the system enables efficient evaluation of the performance of F2 excimer laser lithography processes.

MEASURING SYSTEM FOR SIMULATION PARAMETERS OF CHEMICAL AMPLIFICATION RESIST SYSTEMS

The resolution of a chemically amplified resist tends to be degraded due to postexposure delay (PED). To elucidate the characteristics of the degradation, we conducted studies employing simulations of lithographic processes. In performing such studies, simulation parameters (diffusion length of the photoactive compound, surface inhibition parameters) are normally estimated by calculating the distribution of the photoactive compound concentration in the resist film using Dills ABC parameters for a conventional resist. However, bleaching in many chemically amplified resists does not occur (parameter A = 0), making it difficult to compute the ABC parameters. Therefore, we studied a method of estimating simulation parameters that uses the accumulated exposure energy instead of the concentration distribution of the photoactive compound in the resist film. Simulation parameters were estimated for a t-BOC chemically amplified resist for use with KrF excimer lasers. The values obtained were input to the PROLITH/2 photoresist profile simulator, and profiles were calculated. Pattern calculations assumed a wavelength of 248 nm, with NA = 0.5 and a coherence factor of 0.6, and line and space of 0.25 μm and 0.30 μm. The results were compared with SEM observations to confirm the validity of the method of estimation. Good agreement was found between the simulated results and the SEM observations, confirming the soundness of the estimation method. In addition, simulations confirmed that the cause of resolution deterioration, as PED progresses, is the formation of a surface-inhibiting layer extending deep into the resist film.